This invention relates to a photovoltaic module having a semiconductor layer formed on a glass substrate and sealed by means of a encapsulation material. Known photovoltaic modules include those of the crystal type prepared by using single crystal silicon or polycrystal silicon and those of the amorphous type prepared by using amorphous silicon. In any case, it has to be noted that silicon is apt to chemically react and fragile when subjected to a kinetic impact.
The use of a encapsulation structure has been proposed in order to protect the silicon in the photovoltaic module and electrically insulate the semiconductor layer of the module. According to the proposed encapsulation technique, the encapsulation structure may comprise a encapsulation material typically made of EVA (ethylene-vinyl acetate copolymer) or EVAT (ethylene-vinyl acetate-triallylisocyanurate bridged tripartite copolymer). When encapsulation the semiconductor layer with a encapsulation material, the substrate and the encapsulation material laid on the substrate are normally united by applying pressure and heat.
As the encapsulation material is heated under pressure, it contracts. Therefore, the encapsulation material is sized so as to be greater than the substrate in order to compensate the contraction by heat under pressure. However, the extent of contraction of the encapsulation material by heat under pressure can vary as a function of various factors involved in the heating/pressurizing operation. The net result can often be a peripheral edge of the encapsulation material projecting outwardly beyond its counterpart of the substrate.
When the photovoltaic module is used in a state where the peripheral edge of the encapsulation material is projecting outwardly beyond the counterpart of the substrate, external force can inadvertently be applied to the portion of the encapsulation material projecting beyond the end face of the substrate and a repeated application of such force can eventually damage the periphery of the encapsulation material to separate, at least partly, the encapsulation material from the substrate by a gap, through which rain water can get into the semiconductor layer.
FIG. 14 of the accompanying drawings schematically illustrates a known thin film type photovoltaic module designed to enhance the environment-resistance of the photovoltaic cells. The illustrated photovoltaic module is same as a module disclosed in Japanese Utility Model Application Laid-Open No. 25633877. Referring to FIG. 14, there is shown a front surface glass cover 1 operating as transparent substrate, on the rear surface of which a plurality of thin film type photovoltaic cells 2 are arranged and connected in series and/or in parallel by the rear electrode 3. The rear electrode 3 is connected to an output lead-out wire 4 typically made of metal foil. The rear electrode 3 is sealed by means of a filling member 5. More specifically, the filling member 5 is formed typically by hot-melting EVA, while keeping the related end of the output lead-out wire 4 standing. The rear surface of the filling member 5 is coated with a rear surface encapsulation material (weather-resistant film) 6 having a three-layered structure of sandwiching a metal foil 6a by a pair of insulating films 6b. The rear surface filling member 6 is provided with a through bore operating as an output lead-out section Q for leading the output lead-out wire 4 to the outside. The output lead-out wire 4 is drawn to the rear surface side of the rear surface encapsulation material 6 by way of the through bore. The output lead-out wire 4 drawn to the outside is secured at the leading end thereof to terminal 7 by soldering or by means of a screw. An output lead wire 8 is connected to the terminal 7. The terminal section including the output lead-out wire 4, the terminal 7 and the output lead wire 8 is housed in a terminal box 9.
The exposed areas of the filling member 5 and the output lead-out wire 4 of the output lead-out section Q may be sealed by means of protective resin such as silicon resin. Similarly, the surface of the terminal 8 may be sealed by means of protective resin such as silicon resin.
FIG. 15 of the accompanying drawings schematically illustrates a known crystal type photovoltaic module. Referring to FIG. 15, a plurality of crystal type photovoltaic cells 11 are arranged on the rear surface of a front surface glass cover 1 and connected by connection wires 12. The photovoltaic cell 11 arranged at an end of the module is connected to an output lead-out wire 4 typically made of metal foil. Otherwise, the module of FIG. 15 has a configuration substantially same as the module of FIG. 14.
Neither of the above listed photovoltaic modules is not satisfactory in terms of moisture-resistance and water-resistance because the filling member 5 is exposed to the atmosphere at the output lead-out section Q. If the output lead-out section Q is protected by means of silicon resin or some other protecting material, it not satisfactory either in terms of moisture-resistance and water-resistance because the section Q remains practically exposed to the atmosphere. Thus, particularly if water penetrates into the inside of the terminal box 9, moisture can get into the filling member 5 by way of the output lead-out section Q to consequently corrode the output lead-out wire 4 and the rear electrode 3. This is a major drawback of known photovoltaic modules particularly in terms of environment-resistance. As a matter of fact, most of the troubles that occur in photovoltaic modules are attributable to a corroded rear electrode 3 produced by moisture penetrated into it from the outside.